I'm having the same issues using SFML 2.6. No input from the triggers or dpad is being picked up by SFML, works fine when testing controller using different programs. Is this a known issue?
I should also mention that the Z axis, which is the axis I would have expected the trigger to be registered as, is actually assigned to the right analog stick X axis (so does the horizontal input for the analog stick which uses R for vertical input).